The present invention relates to the polymerization of ethylene in the presence of supported catalysts known in the art as Ziegler catalysts.
Ziegler catalysts are commonly formed by reducing a transition metal compound with an organometallic compound. The reduced transition metal compound is then used, in conjunction with an activator, which may be the same or a different organometallic compound, to polymerize olefins, especially ethylene, in the presence of an inert solvent or in the gas phase. A molecular weight regulator, such as hydrogen, may be used with these catalyst systems, as taught by Vandenberg in U.S. Pat. No. 3,051,690.
Such catalysts are often rather unefficient because the catalyst particles tend to agglomerate. To obviate this problem many systems of supporting the catalyst on solid carriers have been proposed.
Kashiwa et al, in U.S. Pat. No. 3,642,746, describe catalysts utilizing a magnesium chloride support pretreated with an electron donor, such as methanol, and then treated with a titanium compound. The electron donor must be coordinated with the magnesium chloride when the titanium compound is added to the support.
Diedrich et al., in U.S. Pat. No. 3,644,318, describe catalysts supported on magnesium alcoholates.
Stevens et al., in U.S. Pat. No. 3,718,636 describe catalysts obtained by reacting a magnesium oxide support with an organometallic compound, separating the resulting solid product and reacting this product with a titanium compound. The polyethylene produced with this catalyst had low melt index and broad molecular weight distribution.